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| United States Patent |
6,246,005
|
|
Mahlandt
, et al.
|
June 12, 2001
|
Radiating coaxial cable
Abstract
A radiating coaxial high-frequency cable is provided with openings in the
outer conductor which are in the form of slots (5) arranged substantially
perpendicular to the cable axis. The slots (5) are arranged in sections
which are arranged consecutively without gaps in the longitudinal
direction of the cable and whose axial length is dimensioned according to
the high-frequency energy to be transmitted. The number of slots (5) is
greater in the sections which are farther away from the feed location of
the high-frequency energy than in the sections which are closer to the
feed location. When the length of the cable is increased, several sections
(A) with an identical number of slots are arranged consecutively without
gaps, provided that subsequent sections (A) have a larger effectual
opening when the system damping between the high-frequency cable and an
antenna located outside the cable reaches a predetermined value.
| Inventors:
|
Mahlandt; Erhard (Hannover, DE);
Schulze-Buxloh; Karl (Monchengladbach, DE)
|
| Assignee:
|
Alcatel (Paris, FR)
|
| Appl. No.:
|
135935 |
| Filed:
|
August 18, 1998 |
Foreign Application Priority Data
| Sep 03, 1997[DE] | 197 38 381 |
| Current U.S. Class: |
174/102R; 174/102SP |
| Intern'l Class: |
H01B 007/12; H01B 007/18 |
| Field of Search: |
174/102 SC,102 SP,102 R,36
|
References Cited
U.S. Patent Documents
| 3106713 | Oct., 1963 | Murata et al. | 343/770.
|
| 4280225 | Jul., 1981 | Willis | 455/55.
|
| 4322699 | Mar., 1982 | Hildebrand et al. | 333/237.
|
| 4325039 | Apr., 1982 | Allebone | 333/237.
|
| 4800351 | Jan., 1989 | Rampalli et al. | 333/237.
|
| 5276413 | Jan., 1994 | Schulze-Buxloh | 333/237.
|
| 5291164 | Mar., 1994 | Levisse | 333/237.
|
| 5422614 | Jun., 1995 | Rampalli et al. | 333/237.
|
| 5467066 | Nov., 1995 | Schulze-Buxloh | 333/237.
|
| 5705967 | Jan., 1998 | Pirard | 333/237.
|
| 5809429 | Sep., 1998 | Knop et al. | 455/523.
|
| Foreign Patent Documents |
| 41 06 890 | May., 1991 | DE.
| |
| 0 028 500 | May., 1981 | EP.
| |
| 0 502 337 | Sep., 1992 | EP.
| |
| 0 643 438 | Jul., 1994 | EP.
| |
| 0 694 986 | Jul., 1994 | EP.
| |
| 2 420 857 | Dec., 1978 | FR.
| |
Primary Examiner: Dinkins; Anthony
Assistant Examiner: Mayo, III; William H
Attorney, Agent or Firm: Ware, Fressola, Van der Sluys & Adolphson LLP
Claims
What is claimed is:
1. A radiating coaxial cable for transmitting high-frequency energy from a
feed location, comprising:
(a) a central conductor defining a cable axis;
(b) a dielectric surrounding the central conductor; and
(c) an outer conductor which surrounds the central conductor and
dielectric, the outer conductor having sections which are arranged
consecutively without gaps in an axial direction of the cable, all
sections have an equal axial length which is dimensioned according to the
high-frequency energy to be transmitted, the outer conductor having slots
in each section creating an effectual opening in each section, an initial
plurality of the sections of the initial plurality of the sections with
each section therein having an identical number of slots creating an
effectual opening identical in size, the sections in the initial plurality
of the sections arranged consecutively without gaps starting at the feed
location of the high-frequency energy, and at least one subsequent
plurality of sections subsequent to the initial plurality of the sections,
each section in each individual one of the at least one subsequent
plurality of sections having an identical number of slots creating an
effectual opening larger than the effective opening of each section of the
initial plurality of sections and any preceding subsequent plurality of
sections, each section of the at least one subsequent plurality of
sections beginning where system damping between the cable and an antenna
located outside the cable reaches a predetermined value, the initial
plurality of the sections and each section of theat least one subsequent
plurality of sections define a first length having the slots with one slot
size the slots of the one slot size are greater in number in the sections
of the first length which are more distant from the feed location of the
high-frequency energy than in the sections of the first length which are
closer to the feed location and several sections of the first length with
an identical number and arrangement of the slots of the one slot size
directly abut each other at least one additional similarly constructed
length of the outer conductor following the first length the effectual
opening of the slots arranged in each of the sections of the at least one
additional length of the outer conductor is larger than the effectual
opening of the slots in each corresponding section of the first length
wherein the slots in the first length and the at least one additional
length have different sizes the slots for one slot size increase in number
in the sections with increasing distance from the feed location of the
high-frequency energy.
2. The cable according to claim 1, wherein the slots of the different sizes
have a width which is identical in an axial direction of the cable but
different lengths in a circumferential direction of the cable.
Description
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to a radiating coaxial high-frequency cable with
openings in the outer conductor which are in the form of slots arranged
substantially perpendicular to the cable axis and which are configured in
sections which are arranged consecutively without gaps in the longitudinal
direction of the cable and whose axial length is dimensioned according to
the high-frequency energy to be transmitted, wherein the number of slots
is greater in the sections which are farther away from the feed location
of the high-frequency energy than in the sections which are closer to the
feed location.
2. Description of the Prior Art
Radiating coaxial high frequency cables--hereinafter called
"RHF-cables--operate essentially as antennae as a result of the
electromagnetic energy which is transmitted to the outside through the
slots in the outer conductor. These cables enable communication between
transmitters and receivers which move relative to each other. The
intensity of the radiated power decreases along the length of the RHF
cable due to cable damping (longitudinal damping) and because HF energy is
radiated (coupling damping). Consequently, the so-called "system damping"
which is the sum of the longitudinal damping and coupling damping--for
example between an antenna of a vehicle and a RHF cable--increases with
increasing cable length measured from the location where the HF energy is
fed into the RHF cable. To keep the field strength which is received by a
receiver moving along the RHF cable, at least approximately constant, the
effect of the longitudinal damping of the RHF cable described in DE 41 06
890 A1 is compensated with the help of a special slot configuration. The
number of the slots along the cable increases here according to a
predetermined rule. The cable with this configuration can then made longer
than a RHF cable with a uniform slot arrangement. Nonetheless, the length
of the RHF cable along which a "usable" signal can be received or coupled
in, remains relatively short, in particular at higher operating
frequencies.
A conventional RHF cable can operate over a greater length by using the
cable design according to EP 0 643 438 A1. This RHF cable has consecutive
sections wherein each section has a different number of slots. The
electrically effectual size of the openings formed by the slots increases
with increasing distance from the location where the HF energy is injected
into the cable. The longitudinal damping of the longer RHF cable is also
compensated, providing greater flexibility for tuning important properties
of the transmission system. The cable also requires a lesser number of
amplifiers and feed locations along the cable run. This RHF cable has
proven effective in practice. However, the "usable" length of the
cable--as defined above--is still limited, in particular at higher
frequencies.
SUMMARY OF THE INVENTION
It is an object of the invention to improve the RHF cable described above
so as to further increase its length without additional amplifiers and
feed locations, in particular at higher frequencies.
This object is solved with the invention by arranging several sections with
an identical number of slots consecutively without gaps, provided that the
effectual opening of subsequent sections is increased when the system
damping between the high-frequency cable and an antenna located outside
the cable reaches a predetermined value.
The distance which can be covered with the RHF cable designed in this
fashion, can be readily increased without requiring additional amplifiers
or additional injection of HF energy. The effectual opening in the outer
conductor of the RHF cable can be enlarged with increasing distance from
the location where the HF energy is injected, by providing more slots
which can be made of different size. In each section a sufficient number
of larger slots can then advantageously be arranged on the outer conductor
even if the sections of the RHF cable are relatively short in the axial
direction and frequency-dependent. The original goal of attaining a
"larger opening with increasing distance from the feed location" can
thereby be met. In the sections which have a greater distance from the
feed location, only slots which are quite long in the direction of the
circumference, are provided in the outer conductor. A RHF cable designed
in this fashion is easier to manufacture since, for example, only two
different stamping tools are required to machine the slots. The smaller
slots can be stamped first, while the longer slots are stamped later. It
is possible to interleave sections with slots of different slot lengths.
The invention will be fully understood when reference is made to the
following detailed description taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic side view of a RHF cable according to the invention,
FIG. 2 is a schematic diagram of an arrangement of slots in the outer
conductor of the RHF cable, and
FIGS. 3 and 4 are schematic diagrams of a representation an arrangement of
slots in the outer conductor of the RHF cable.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a RHF cable which can be installed, for example, in a railway
tunnel to transmit signals between stationary units and mobile units. The
RHF cable has an inner conductor 1, a dielectric 2 and a tubular outer
conductor 3 which concentrically surrounds the inner conductor 1. The
outer conductor 3 is, for example, a longitudinal metal tape which is
applied around the dielectric 3 in a way that the lateral tape edges
overlap. The edges can be joined, for example, with an adhesive, by
soldering or by welding. The lateral edges of the tape can also be welded
to each other without overlap. A jacket 4 which is made of plastic and
which can be flame-retardant, provides mechanical protection on the
outside.
The inner conductor 1 and the outer conductor 3 are preferably made of
copper. The dielectric 2 can be fabricated by conventional processes, i.e.
it can be a tightly packed dielectric, including foam, or a hollow
dielectric, including a helix or disks. The dielectric 2 is preferably
made of materials with a small dielectric loss factor, for example
polyethylene. The jacket 4 can be made of, for example, polyethylene or
polyvinylchloride.
The outer conductor 3 is provided with slots 5 which in the illustrated
embodiment are longer in the direction of the circumference than they are
wide in the axial direction. The outer conductor 3 has a number of
sections A which are arranged consecutively without gaps in the
longitudinal direction of the RHF cable. Several sections A with the same
number of slots 5 are arranged immediately adjacent to each other. Due to
the slots 5, HF energy can be received outside the RHF cable with a
suitable antenna. It is equally possible to couple HF energy into the RHF
cable in the opposite transmission direction.
The number of slots 5 per unit length increases with increasing distance
from the feed location E of the HF energy. The received signal has then an
essentially constant level along the entire length of the RHF cable. This
is illustrated schematically in FIG. 2 for only one section A by way of
example. A unit length of the RHF cable includes all respective sections A
which have the same number of slots 5. The axial length of the sections A
depends on the frequency of the HF energy which is injected into the RHF
cable. The sections A become shorter with increasing frequency. However,
the basic design and arrangement of the slots 5 is presumed to be
identical for all embodiments. The number of slots 5 for each section A is
increased at regular intervals when the level of the received signal has
reached or dropped below a predetermined value. In this way, the system
damping between the RHF cable and an antenna located or moving outside the
RHF cable can be very accurately maintained at a predetermined value.
For example, a RHF cable with slots 5 arranged in section A according to
the schematic diagram of FIG. 2 has, for example, the following form:
In the present example, a section A designed for the frequency range 1800
MHz (1710 MHz to 1920 MHz) as a length of the 8.5 cm. Sections A are
arranged consecutively without gaps along a length (hereinafter referred
to as unit length) of approximately 100 m, wherein each of the sections A
has one slot 5. As a result, approximately 590 sections with only one slot
5 are arranged sequentially. Directly following, without a gap, is a
length of approximately 90 m which has two slots 5 per section A, for a
total of approximately 530 sections A. Each section A of the subsequent
unit length of approximately 75 m has four slots, for a total of
approximately 440 sections A. The final portion of the cable is formed by
a unit length of approximately 55 m, wherein each section A has eight
slots 5. This unit length then has approximately 320 sections A. The
entire length of the corresponding RHF cable is approximately 320 m.
In FIG. 3, there is illustrated a preferred embodiment for arranging the
slots 5 in the outer conductor 3. All sections A have once again the same
axial length. In this embodiment, the RHF cable can have a total length of
approximately 500 m. Only two different slot sizes are used. The small
slots are indicated with the reference numeral "6" and the large slots
with the reference numeral "7". All slots 6 and 7 have preferably the same
width in the axial direction. The slots 7 are longer in the direction of
the circumference of the RHF cable than the slots 6. For each respective
number of slots, only one section A is shown in FIG. 3. This embodiment
again has a large number of identically constructed and consecutively
arranged sections A, as was described above with reference to the example
of FIG. 2.
Since the HF signal is strongest at the beginning of the RHF cable, i.e.
proximate to the location E where the HF energy is injected, the outer
conduct 3 in this region need only have a small clear opening. Each
section A therefore has only two slots 6. Several sections A with only two
slots 6 each are then arranged consecutively until the level of the
received signal reaches a predetermined lower limit. The subsequent
sections A then have four slots 6 each. The sections A thereafter have
eight slots 6, followed by sections A with sixteen slots 6. The subsequent
sections A with the slots 7 have the same arrangement and sequence of
slots. The outer conductor 3 in the terminal sections A has sixteen slots
7. The combined effectual electrical size of the two larger slots 7 which
are located in a section with only two slots, is greater than the combined
clear opening of the sixteen smaller slots 6 located the in the previous
sections.
FIG. 4 shows a complete layout of the embodiment of the slot arrangement
suggested in FIG. 3. A suitable number of respective sections A1 to A8
which each have a different number of slots 6 and 7, is arranged
consecutively. The illustration of FIG. 3 shows only the slot arrangement
for the individual sections.
In the embodiment illustrated in FIG. 4, the distance between the two slots
S1 and S2 in section A1 is fixed. The distance corresponds, for example,
to a quarter of the wavelength of the HF energy to be transmitted. This
distance is maintained for the sections A2 to A8. At most sixteen slots 6
can then be arranged in sections A4 and A8, even if the respective section
itself is longer. Because of the limited space, only seven slots 6 and 7,
respectively, fit between the two slots S1 and S2. A total of sixteen
slots 6 and 7, respectively, can be accommodated because of the symmetry
of this arrangement.
The configuration of slots 6 and 7 differ from the arrangement illustrated
in FIG. 4 for different wavelengths of the HF energy which is to be
transmitted. For example, it is possible to have only one slot in each of
the first sections A. The number of slots which can be arranged next to
each other in each of the terminal sections A is only limited by the
available space, i.e. the entire length of these sections A can be filled
with slots 6 and 7, respectively.
In the embodiment of FIGS. 3 and 4, the sections A1 to A4 have exclusively
smaller slots 6 whereas the subsequent sections A5 to A8 have exclusively
larger slots 7. It will be understood by those skilled in the art that
large slots 7 can also be used in the sections A2 to A4 if the large slots
7 in the outer conductor 3 have the same clear opening as the slots 6.
It is also possible to use more than two different slots sizes. The slots
can then be arranged on the outer conductor 3 either according to
size--similar to the arrangement depicted in FIGS. 3 and 4--or the slots
can be interleaved. The length of the sections A can also vary, with the
respective slot arrangements spaced closer to each other or farther apart
from each other.
The RHF cable is preferably manufactured from a metal tape adapted to form
the outer conductor 3, wherein the slots 5, 6 and 7, respectively, are
formed in the metal tape already during preproduction. The respective
slots are punched out of the metal tape in a continuous pass.
The embodiments described above admirably achieve the objects of the
invention. However, it will be appreciated that departures can be made by
those skilled in the art without departing from the spirit and scope of
the invention which is limited only by the following claims.
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